Digestive System Evolution The digestive systems of mammals and other invertebrates are all similar, and yet in their own way quite different. Most invertebrates have adaptations in their digestive system to fit their diet.
Hydra have an inner gastrodermis that is specialized for digestion. Enzymes released from gland cells into the gastrovascular cavity initiate digestion, which is completed intracellularly after small food particles are taken into nutritive cells by phagocytosis. Undigested waste is egested through the mouth, the single opening of the gastrovascular cavity.
The sponge is a suspension feeder that captures small food particles suspended in the large volumes of water that are swept through the body through small pores. Flagellated cells called choanocytes contribute to water from and also trap food particles in mucus-covered collars surrounding the bases of the flagella. The choanocytes then engulf the food by phagocytosis, and intracellular digestion occurs within food vacuoles. The contents of some food vacuoles are transferred to wandering amoebocytes, which in turn distribute food to other cells of the sponge.
The digestive system of an earthworm consists of five organs. A muscular pharynx sucks food in through the mouth. Food passes through the esophagus and it stored and moistened in the crop. The muscular gizzard, which contains small bits of sand and gravel, pulverizes the food. Digestion and absorption occurs in the intestine, which has a dorsal fold, the typhlosole, that increases surface area for nutrient absorption. The undigested material is expelled through the anus.
The grasshopper has several digestive chambers grouped into three main regions: a forgut, midgut, and a hindgut. Food is stored and moistened in the crop, but most digestion occurs in the stomach. Gastric ceca, pouches extending from the stomach, transfer nutrients to the grasshopper's hemolymph (blood).
The bird has three separate chambers- the crop,